Additive for reducing the roasting temperature of fluxed magnetite pellets and a method of using it

ABSTRACT

The present invention discloses additive for reducing the roasting temperature of fluxed magnetite pellets and a method of using it, consisting of components: B2O3, Mn2O3, the B2O3 and Mn2O3 are pure chemical reagents, the mass of the additive is 0.8%, 4% of the dry basis mass of the magnetite concentrate, respectively, the magnetite concentrate, bentonite clay, calcium flux and additives will be dosed with 12-14% water of the dry base mass ratio of the mixture, prepared into green pellets of 10-12.5 mm in diameter in a disc ball making machine. After the pellets are completely dried, preheat them for 15˜20 min at 600˜1000 ° C. to ensure that Mn2O3 is fully decomposed, then roasting is carried out for 15 min at 1200 ° C., and after roasting, the pellets are cooled to room temperature to obtain the finished pellets.

TECHNICAL FIELD

The present invention relates to a magnetite concentrate pellet roasting additive, in particular to an additive for reducing the roasting temperature of magnetite concentrate pellets, and also relates to a method of using additives to reduce the roasting temperature of fluxed magnetite concentrate pellets, belonging to the field of iron and steel metallurgy.

BACKGROUND TECHNOLOGY

As the largest emission of harmful dust gases in the steel process, the pre-iron process hinders low-carbon environmental protection work, and the sinter and pellet ore, which are the main raw materials for production are the key factors. The energy consumption of pellet ore production is about ½ of the sintering process compared to sintered ore, the emissions of dust, SO₂ and NO. are about 1/7, ⅓ and ⅕ of the sintering process, respectively, and the pellet production process produces almost no dioxins, that it is more in line with the national call for energy conservation and emission reduction requirements. Therefore, reducing the amount of sinter used and increasing the proportion of pellets in the furnace is a green development path for today's steel industry.

In order to meet the demand for blast furnace ironmaking and increase the proportion of pellets in the furnace, the focus of research has gradually shifted to flux pellets in recent years. Due to the addition of calcium fusible pellets, low melting point substances such as calcium ferrate and fayalite are easily generated during high temperature roasting process, resulting in a high amount of liquid phase which makes the roasting process produce adhesion phenomenon, which is difficult to control in actual production. In order to mitigation the roasting adhesion problem of molten pellets, the performance of molten pellets was mostly improved by adding magnesium-containing melting flux to promote the production of high melting point substances. Prior art solutions:

Program I: The return sinter fines, slaked lime and sodium humate were mixed, aged and ball milled as compound additives and added to the pellet raw material for pellet making and pellet preheating roasting experiments, which reduced the pellet roasting temperature by 30 to 50° C. In program 1 low temperature roasting additives generally need to be prepared in advance, and the additives contain a small amount of alkali metal Na+, the actual industrial production process may have an impact on the blast furnace downstream.

Program II: Separate the pellets in the roasting process by adding a certain size of titanium slag to the rotary kiln to reduce the pellet ore bonding rate and alleviate the rotary kiln ringing condition. In program 2 is to alleviate the roasting bonding problem between pellets by adding external factors, only to a certain extent to suppress the phenomenon of rotary kiln ringing, and does not fundamentally solve the pellet ore roasting bonding problem and titanium slag particle size is fine, there may be a trace of titanium slag adsorbed on the surface of the pellet ore, which affects the quality of the pellet ore.

Program III: By optimizing the thermal parameters of the fine-grained magnetite pellet roasting process, such as air temperature, heating speed, material layer height, grate running speed and oxygen content in the roasting atmosphere, etc., and controlling the oxidation ratio of pellets in the preheating, roasting and cooling sections, deep oxidation and efficient consolidation of pellets are realized. Finally, when the rotary kiln roasting temperature was 1200° C., the average compressive strength of pellet ore reached 2779 N/pc. Although program 3 promoted the deep consolidation of pellet ore by changing the thermal parameters and obtained iron ore pellets with higher strength, this optimization scheme is not necessarily applicable to other types of magnetite ores.

Program IV: After the magnesium flux lightly burned dolomite and water fully digestion, according to a certain weight ratio of the above magnesium additives and magnetite concentrate, bentonite for mixing, balling, roasting and cooling, roasting temperature 1190° C. at 9 min roasting to make a high quality magnesium pellet ore with a compressive strength of 22002400N/pc. Program 4 adds MgO flux to the raw material although it can generate high melting point material and reduce the bonding problem to some extent, but the addition of Mg2+ will cause it to enter the magnetite lattice and hinder the magnetite oxidation recrystallization to some extent, and the addition of MgO flux should not be too high, so it also has some disadvantages.

INVENTION CONTENT

In response to the existing problems of high roasting temperature of oxidized pellets prepared from high-silica magnetite concentrate and low product strength, the present invention provides an additive to reduce the roasting temperature of magnetite concentrate pellets, which can significantly reduce the pellet roasting temperature and lower the pellet roasting temperature by 50-80° C. on average, which can significantly reduce the production energy consumption, improve the pellet strength index and alleviate the high temperature roasting bonding phenomenon.

To achieve the above technical purpose, the present invention provides an additive for reducing the roasting temperature of magnetite concentrate pellets, consisting of components: B₂O₃, Mn₂O₃. B₂O₃ and Mn₂O₃ are chemical reagents analytically pure, and the additive consists of a mixture of B₂O₃ and Mn₂O₃, where the mass percentage of B₂O₃ is 0.8% of the dry basis mass of magnetite concentrate, and the mass percentage of Mn₂O₃ The mass percentage of B₂O₃ is 0.8% of the dry mass of magnetite concentrate and the mass percentage of Mn₂O₃ is 4% of the dry mass of magnetite concentrate.

The present invention is the same as the common iron ore pellet roasting process of the prior art, except that the preheating time is appropriately extended when the preheating temperature band is 600-1000° C. in the preheating process, mixing, pelletizing, drying and oxidation roasting. The magnetite concentrate, 0.7% of bentonite, calcium flux and additives into a mixture, with a mixture of dry mass ratio of 12˜14% of water, in the disc ball making machine to prepare the diameter of 10˜12.5 mm raw ball, after the raw pellets are completely dried, they are preheated at 600-1000° C. for 15-20 min to ensure the full decomposition of Mn₂O₃, and then roasted at 1200° C. for 15 min, after the roasting is completed, the pellets are cooled to room temperature to obtain the finished pellet ore. The reference pellets without the addition of B₂O₃ and Mn₂O₃ were then subjected to high-temperature (1250-1280° C.) preheat roasting experiments, and compressive strength tests and mineral phase structure observations were conducted at the end of the tests.

Compared with the prior art, the technical solution of the present invention brings beneficial technical effects: the greatest advantage of the technical solution of the present invention is that the use of additives can significantly reduce the pellet roasting temperature, the average pellet roasting temperature is reduced by 50-80° C., which can significantly reduce the production energy consumption and improve the pellet strength index, additives in the present invention to reduce the roasting temperature of magnetite concentrate pellets include B₂O₃, Mn₂O₃ chemical reagent analysis pure, the roasting temperature is set below the melting point temperature of low melting point substances, i.e. 1200° C, the melting temperature of B₂O₃ is 450° C., which provides trace fluid phase for pellets to promote Fe2+ movement and accelerate solid-phase consolidation during the preheating process. The heating decomposition equation of Mn₂O₃ in the literature “Study on the kinetics of low temperature decomposition of manganese dioxide” is as follows: 6Mn₂O₃→4Mn₃O₄+O₂, and the experimental TG curve of thermal gravimetric analysis of Mn₂O₃, as shown in FIG. 2 , the TG curve indicates that the temperature interval of Mn2O3 during the warming process is 600-1000° C. with slow weight loss decomposition, which coincides with the preheating temperature interval of magnetite pellets under normal conditions. The slow release of O₂ during preheating promotes the oxidative recrystallization of magnetite from within.

ILLUSTRATED CATALOGUE

FIG. 1 : Flow chart of the pellet production process of the present invention.

FIG. 2 : Experimental TG curve of thermal gravimetric analysis of the present invention.

SPECIFIC EMBODIMENT

Referring to the attached FIG. 1 pellet ore production process for implementation

EXAMPLE 1

Using local high-silica magnetite concentrate (TFe66.3%, SiO2 content 6.17%) was used as raw material, 0.7% bentonite and calcium flux CaO were added and mixed, no B₂O₃, Mn₂O were added, after adding 12˜14% moisture, the raw balls of 10˜12.5 mm in diameter are prepared in the disc ball making machine, the falling strength of raw balls is 5 times/ball (0.5 m), the compressive strength of raw balls is 8.2N, after the raw balls are dehydration and dried, the preheating temperature is 900° C., the preheating time is 15 min, the roasting temperature is 1200° C., the roasting time is 15 min. the average strength of the roasted finished balls is 1980N/pc, and the strength of the pellet ore is lower at this time.

EXAMPLE 2

Using local high-silica magnetite concentrate (TFe66.3%, SiO2 content 6.17%) as raw material, adding 0.7% bentonite, calcium flux CaO, 4% Mn2O3 for mixing, without adding B₂O₃. after adding 12˜14% moisture, the raw balls of 10˜12.5 mm in diameter are prepared in the disc ball making machine, the falling strength of raw balls is 5 times/ball (0.5 m), the compressive strength of raw balls is 8.4N, after the raw balls are dehydration and dried, the preheating temperature is 600˜1000° C., the preheating time is 15 min, the roasting temperature is 1200° C., the roasting time is 15 min. the average strength of the roasted finished balls is 2274N/pc, and the strength of the pellet ore is slightly higher at this time.

EXAMPLE 3

Using local high-silica magnetite concentrate (TFe66.3%, SiO2 content 6.17%) as raw material, adding 0.7% bentonite, calcium flux CaO, 0.8% B₂O₃ and then mixing, without Mn₂O₃. after adding 12˜14% moisture, the raw balls of 10˜12.5 mm in diameter are prepared in the disc ball making machine, the falling strength of raw balls is 6 times/ball (0.5 m), the compressive strength of raw balls is 9.1N, after the raw balls are dehydration and dried, the preheating temperature is 900° C., the preheating time is 15 min, the roasting temperature is 1200° C., the roasting time is 15 min. the average strength of the roasted finished balls is 2631N/pc, and the strength of the pellet ore is higher at this time.

EXAMPLE 4

Using local high-silica magnetite concentrate (TFe66.3%, SiO2 content 6.17%) as raw material, add 0.7% bentonite, calcium melt CaO, 0.8% B₂O₃, 4% Mn2O3 and mix well, after adding 12˜14% moisture, the raw balls of 10˜12.5mm in diameter are prepared in the disc ball making machine, the falling strength of raw balls is 6 times/ball (0.5 m), the compressive strength of raw balls is 9.3N, after the raw balls are dehydration and dried, the preheating temperature is 600˜1000° C., the preheating time is 15 min, the roasting temperature is 1200° C., the roasting time is 15 min. the average strength of the roasted finished balls is 2962N/pc, and the strength of the pellet ore is very high at this time.

EXAMPLE 5

Using local high-silica magnetite concentrate (TFe66.3%, SiO2 content 6.17%) was used as raw material, 0.7% bentonite and calcium flux CaO were added and mixed, no B₂O₃, Mn₂O were added, after adding 12˜14% moisture, the raw balls of 10˜12.5 mm in diameter are prepared in the disc ball making machine, the falling strength of raw balls is 6 times/ball (0.5 m), the compressive strength of raw balls is 9.5N, after the raw balls are dehydration and dried, the preheating temperature is 900° C., the preheating time is 15 min, the roasting temperature is 1280° C., the roasting time is 15 min. the average strength of the roasted finished balls is 3063N/pc, and the strength of the pellet ore strength at this time.

Macro strength indicates: B₂O₃ and Mn₂O₃ have a promoting effect on the oxidative recrystallization process of magnetite at low temperature, but the promotion methods are different. among them, Mn₂O₃ promotes the oxidation and recrystallization of magnetite from the gas phase, and B₂O₃ promotes the movement of Fe2+ from the liquid phase to accelerate the solid-phase consolidation. The combined promotion effect of the additive was greater than that of the single additive, and the macroscopic strength results showed that the compressive strength of pellet ore at 1200° C. after adding the additive was basically the same as the compressive strength of pellet ore in the roasted specimens at 1250-1280° C.

The traditional method to reduce the bonding rate of fusible pellets by high temperature roasting is to add MgO fusible to the pellets to produce a high melting point substance, which makes it unsuitable for bonding at high temperatures. Traditional oxidation roasting of magnetite pellets is carried out layer by layer from the outside to the inside. Calcium ferrate systems such as CaO·Fe₂O₃, CaO·2Fe₂O₃, CaO·Fe₂O₃-CaO·2FeO eutectic mixtures, which all have low melting points of 1216° C., 1226° C. and 1205° C. respectively, can play a role in promoting the bonding of iron ore particles and increasing the strength of pellets with the moderate amount of liquid phase during the high temperature oxidation roasting of pellets. However, in the pellet roasting process, the amount of liquid phase not only needs to be strictly controlled, but also the amount of calcium ferrate liquid phase is difficult to control, and too much liquid phase will lead to pellet bonding and porosity reduction, but worsen the pellet metallurgical properties.

The present invention starts from the root cause by adding other additives to increase the strength of the pellets as much as possible while appropriately lowering the pellet roasting temperature, fundamentally control the amount of liquid phase generation at high temperatures to avoid bonding problems, while reducing the roasting temperature of pellet ore is also conducive to energy saving and consumption reduction, prolonging the service life of equipment and ensuring the smooth roasting process, which is of great significance to the industrial production of pellet ore. 

1. An additive that reduces the roasting temperature of fluxed magnetite pellets, wherein it is composed of components: B₂O₃, Mn₂O₃, the B₂O₃, Mn₂O₃ are pure chemical reagents, the additive is mixed with B₂O₃ and Mn₂O₃, wherein the mass percentage of B₂O₃ is 0.8% of the dry base mass of the magnetite concentrate, and the mass percentage of Mn₂O₃ is 4% of the dry base mass of the magnetite concentrate, appropriately extend the preheating time of 600˜1000 ° C. in the preheating temperature section, so that Mn₂O₃ slowly loses weight and decomposes at 600˜1000 ° C. and slowly releases O₂, promotes the oxidative recrystallization of magnetite from the inside, and sets the roasting temperature below the melting point temperature of low melting point substances below 1200° C.
 2. A method for using an additive that reduces the roasting temperature of flux magnetite pellets according to claim 1: the magnetite concentrate, bentonite clay, calcium flux and additives will be dosed with 12-14% water of the dry base mass ratio of the mixture, prepared into green pellets of 10-12.5 mm in diameter in a disc ball making machine, After the pellets are completely dried, preheat them for 15˜20 min at 600˜1000° C. to ensure that Mn₂O₃ is fully decomposed, then roasting is carried out for 15 min at 1200° C., and after roasting, the pellets are cooled to room temperature to obtain the finished pellets.
 3. A method of using an additive for reducing the roasting temperature of fluxed magnetite pellets as claimed in claim 3: characterized in that said bentonite clay is 0.7% of the dry basis mass of the mixture. 